JP5732335B2 - Successive comparison type AD conversion method and apparatus - Google Patents

Description

  The present invention relates to a successive approximation AD conversion method and apparatus for AD converting a detection signal of a sensor that outputs a measurement value of a physical phenomenon as an electric detection signal.

  A general successive approximation AD converter is configured, for example, as shown in FIG. In this successive approximation AD converter, the actual measurement detection signal of the bridge sensor B1 that outputs the measurement result of the physical phenomenon as an electrical signal is compared with the reference voltage VCOM by the high gain differential amplifier 2 via the multiplexer 12. Thus, a signal voltage Vop is obtained, and the signal voltage Vop is sampled and held by the sample hold circuit 4 of the successive approximation type AD conversion main body 3, and this is converted into a voltage obtained by DA-converting the immediately preceding AD conversion data by the DA converter 7. The comparison is made by the comparator 5 and the comparison result is stored in the successive approximation register 6. By repeating the comparison in the comparator 5 and the storage in the successive approximation register 6 for the same sample and hold voltage, the bridge sensor B 1 The actual measurement detection signal is output as AD conversion data having a predetermined number of bits.

  In this successive approximation AD converter, in order to compensate for the offset of the high gain differential amplifier 2 and the offset of the successive approximation AD converter body 3, it is used for the AD conversion operation of the actual measurement detection signal of the bridge sensor B1. Prior to this, the multiplexer 12 is switched to the wavy line side, and an initial bias (= 0 V) is input as the bias voltage Vr. At this time, the AD conversion data having a predetermined number of bits stored in the successive approximation register 6 is converted into the reference voltage encoder 13 analog signal. This is input as a reference voltage VCOM for offset compensation to the high gain differential amplifier 2 via the buffer 9, and the offset component is canceled here (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 01-166620

  However, a multi-input AD converter such as a three-axis using a plurality of bridge sensors or the like needs to compensate for the offset in the entire system including the offset of the bridge sensor. In the successive approximation AD converter of FIG. Since the initial bias (= 0 V) is input as the bias voltage Vr from the multiplexer 12, the offset correction in the entire system including the bridge sensor B1 cannot be performed.

  Further, since the detection signal of the bridge sensor is weak, it is essential to insert the high gain differential amplifier 2 as shown in FIG. 3, but in this case, the offset of the bridge sensor B1 and the high gain differential are required. Since the offset of the amplifier 2 and the offset of the successive approximation AD conversion main body 3 are added, a large offset that greatly impairs the dynamic range occurs.

  Further, in the successive approximation AD converter of FIG. 3, when performing high-precision offset compensation, it is necessary to take a fine correction width (resolution), and accordingly, a large number of circuit elements constituting the reference voltage encoder 13 are required. The area when integrated circuits are increased.

  A first object of the present invention is to provide a successive approximation AD conversion method and apparatus capable of offset compensation in the entire system and securing a dynamic range. A second object is to provide a successive approximation AD conversion method and apparatus that can realize offset compensation with high accuracy without increasing the circuit scale.

In order to achieve the above object, the successive approximation AD conversion method according to the first aspect of the present invention compares and amplifies a detection signal of a sensor that outputs a measured value of a physical phenomenon as an electrical detection signal with a reference voltage, In the successive conversion AD conversion method for obtaining AD conversion data by performing AD conversion of the comparatively amplified voltage using a successive approximation type, when a non-measurement detection signal is input from the sensor, in the first cycle, as the reference voltage, The first voltage is set to obtain the AD conversion data, and in the nth cycle (n is a positive integer less than or equal to 2 (m is a positive integer greater than or equal to 3)), the (n-1) th cycle. The nth voltage obtained by raising or lowering the n−1 voltage by a predetermined voltage as the reference voltage so that the AD conversion data approaches a zero value in accordance with the polarity bit of the AD conversion data obtained in step 1). Set Thus, the AD conversion data of the nth cycle is obtained, and in the mth cycle, the AD conversion data approaches a zero value according to the polarity bit of the AD conversion data obtained in the m−1th cycle. The mth voltage obtained by raising or lowering the m−1 voltage by the predetermined voltage is set as the reference voltage, and when the actual measurement detection signal is input from the sensor, the mth voltage is used as the reference voltage. A successive conversion AD conversion method for obtaining the AD conversion data by setting the voltage of the sensor, wherein a plurality of the sensors are provided, each sensor is switched and processed in each cycle, and an actual measurement detection signal is output from the sensor. When inputting, the m-th voltage of the sensor is set as the reference voltage.
The invention according to claim 2 is obtained when the mth voltage is set as the reference voltage when a non-measurement detection signal is input from each sensor in the successive approximation AD conversion method according to claim 1. The AD conversion data is stored as offset data for each sensor, and when the actual measurement detection signal is input from the sensor, the offset data corresponding to the sensor is subtracted from the AD conversion data corresponding to the sensor. It is characterized by that.
A successive conversion AD converter according to a third aspect of the invention includes a sensor that outputs a measured value of a physical phenomenon as an electrical detection signal, a high-gain differential amplifier that compares and amplifies the detection signal of the sensor with a reference voltage, When a non-measurement detection signal is input from the sensor in a successive approximation type AD conversion apparatus including a successive approximation type AD conversion main body unit that AD converts the output voltage of the high gain differential amplifier and outputs AD conversion data A reference voltage encoder that raises or lowers the reference voltage at a predetermined voltage pitch according to a polarity bit of AD conversion data output from the successive approximation AD conversion main body, and the reference voltage encoder when the measurement detection signal is input, in the first cycle, to set the first voltage as the reference voltage, the first n (n is 2 or more m (m 3 or more positive integer) In the cycle of a positive positive integer), the reference voltage is set to the nth-threshold so that the AD conversion data approaches a zero value according to the polarity bit of the AD conversion data obtained in the (n-1) th cycle. The nth voltage obtained by raising or lowering the voltage of 1 by a predetermined voltage is set, and in the mth cycle, the AD conversion data according to the polarity bit of the AD conversion data obtained in the m−1th cycle When the mth voltage obtained by raising or lowering the m-1 voltage by the predetermined voltage is set as the reference voltage so that the value approaches the zero value , and the actual measurement detection signal is input from the sensor, A successive approximation AD converter that sets the mth voltage as the reference voltage, wherein a plurality of the sensors are provided, and each sensor is switched and processed in each cycle. When the measurement detection signal is inputted, wherein the voltage of the m-th of the sensor is set to the reference voltage encoder as the reference voltage.
According to a fourth aspect of the present invention, in the successive approximation AD converter according to the third aspect, when a non-measurement detection signal is input from each of the sensors, the mth voltage is supplied to the reference voltage encoder as the reference voltage. The AD conversion data obtained when set is stored as offset data for each sensor and stored in the offset register corresponding to the sensor when an actual measurement detection signal is input from each sensor. And a plurality of data differentiators for subtracting the offset data from the AD conversion data corresponding to the sensor.

According to the present invention, since the reference voltage is set so that the output voltage of the high-gain differential amplifier when the actual measurement detection signal of the sensor is input approaches the intermediate voltage, the dynamic range of AD conversion can be maximized. it can. Further, since the reference voltage is set to an optimum value according to the offset, the offset of the entire system including the sensor, the high gain differential amplifier, and the successive approximation AD conversion main body can be compensated. In addition, since offset data is subtracted from AD conversion data when an actual measurement detection signal is input, offset compensation can be realized with high accuracy without reducing the resolution of the reference voltage, and the area when integrated circuits are increased. Can be avoided. Further, when a plurality of sensors are used, a reference voltage is set and offset data is stored according to each sensor, and accurate offset compensation can be realized.

1 is a functional block diagram of a successive approximation AD converter according to an embodiment of the present invention. It is operation | movement explanatory drawing of the successive approximation type AD converter of FIG. It is a functional block diagram of a conventional successive approximation AD converter.

  FIG. 1 shows a successive approximation AD converter according to an embodiment of the present invention. A multi-input multiplexer 1 includes switches S1 to Sn for switching output of detection signals of n-channel bridge sensors B1 to Bn. Reference numeral 2 denotes a high gain differential amplifier, which includes an operational amplifier OP and resistors R1 to R4, and compares and amplifies one detection signal of the bridge sensors B1 to Bn selected by the multi-input multiplexer 1 with a reference voltage VCOM.

  Reference numeral 3 denotes a successive approximation AD conversion main body, which includes a sample hold circuit 4, a comparator 5, a successive approximation register 6, and a DA converter 7. The sample hold circuit 4 samples the output signal Vop of the high gain differential amplifier 2 and holds it until a plurality of successive approximation AD conversion operations for obtaining one AD conversion data are completed. The comparator 5 compares the analog voltage output from the DA converter 7 with the output voltage of the sample hold circuit 4. The successive approximation register 6 determines to update the register contents according to the comparison results of the comparator 5 a plurality of times.

  Reference numeral 8 denotes a reference voltage encoder for n channels. When the most significant bit (polarity bit) MSB of the AD conversion data output from the successive approximation AD conversion main body 3 is “1” (polarity is negative) for each channel. Increases the output voltage by 100 mV from the current value, and decreases it by 100 mV when it is “0” (polarity is positive). Reference numeral 9 denotes a buffer which inputs the output voltage of the reference voltage encoder 7 and outputs the reference voltage VCOM. However, the reference voltage VCOM is limited to a maximum value of 300 mV and a minimum value of −300 mV.

  Reference numeral 10 denotes an offset register group including offset registers for n channels, and stores AD conversion data (that is, offset data) of each channel that is AD-converted by inputting a non-measurement detection signal (that is, an offset signal). . 11 is a data differentiator for n channels, and subtracts the offset data of the channel of the offset register group 10 from the AD conversion data output from the successive approximation AD conversion main body 3 for each channel, thereby obtaining the final of the channel. Typical AD conversion data is output.

  In the successive approximation AD converter according to this embodiment, prior to the successive comparison AD conversion operation performed by inputting the actual measurement detection signals of the bridge sensors B1 to Bn, the non-measurement detection signal is input and the reference voltage VCOM is input. And offset data of each channel of the offset register group 10 are set. In FIG. 2, when the bridge sensor has three channels B1 to B3, the output voltage Vop of the high gain differential amplifier when the non-measurement detection signal of the bridge sensor B1 is input is 500 mV, and when the non-measurement detection signal of the bridge sensor B2 is input. The operation explanatory diagram in each case is shown in which the output voltage Vop of the high gain differential amplifier is 300 mV and the output voltage Vop of the high gain differential amplifier when the non-measurement detection signal is input to the bridge sensor B3 is −200 mV.

  First, the reference voltage VCOM is set to an initial state (here, 0 V), and the first cycle of offset measurement is started. At this time, only the switch S1 of the first channel of the multi-input multiplexer 1 is turned on, and the output voltage Vop (= 500 mV) of the high gain differential amplifier 2 obtained by amplifying the non-measurement detection signal of the bridge sensor B1 is the successive approximation type. AD conversion is performed by the AD conversion main body 3, and the AD conversion data at that time is stored in the offset register for the first channel of the offset register group 10. Next, only the switch S2 of the second channel of the multi-input multiplexer 1 is turned on, and the output voltage Vop (= 300 mV) of the high gain differential amplifier 2 obtained by amplifying the non-measurement detection signal of the bridge sensor B2 is the successive approximation type AD. AD conversion is performed by the conversion main unit 3, and the AD conversion data at that time is stored in the offset register for the second channel of the offset register group 10. Next, only the switch S3 of the third channel of the multi-input multiplexer 1 is turned on, and the output voltage Vop (= −200 mV) of the high gain differential amplifier 2 obtained by amplifying the non-measurement detection voltage of the bridge sensor B3 is the successive approximation type. AD conversion is performed by the AD conversion main body 3, and the AD conversion data at that time is stored in the offset register for the third channel of the offset register group 10.

  As described above, AD conversion of the output voltage Vop of the high gain differential amplifier 2 for all three channels at the time of inputting the non-measurement detection signal is completed, and each AD conversion data is stored in the offset register group 10 as offset data. Then, the second cycle of offset measurement is started.

  In the second cycle, the most significant bit MSB of the offset data of the offset registers of the first to third channels of the offset register group 10 is read into the reference voltage encoder 8. In the case of the first and second channels, since the output voltage Vop at the previous cycle was 500 mV and 300 mV, both are MSB = “0”, but at the third channel, the output at the previous cycle Since the voltage Vop is −200 mV, MSB = “1”. The reference voltage encoder 8 increases the reference voltage VCOM output from the buffer 9 by 100 mV when MSB = 1, and decreases the reference voltage VCOM by 100 mV when MSB = 0. The reference voltage VCOM at the time is -100 mV in all cases, but the reference voltage VCOM in the third channel is 100 mV. As a result, the output voltage Vop for the first and second channels is 400 mV, and the output voltage Vop for the third channel is −100 mV.

  In this way, the reference voltage VCOM is switched for each channel, AD conversion of the output voltage Vop of the high gain differential amplifier 2 for all three channels is performed, and the AD conversion data is converted to the offset of each channel of the offset register group 10. Update and store as offset data in the second cycle in the register. Thereafter, the same operation is repeated until the third to fifth cycles of offset measurement. In the fifth cycle, the reference voltage VCOM for the first channel has not changed from -300 mV in the previous fourth cycle, but this is because -300 mV is the limit value. is there.

  As a result, the output voltage Vop of the high gain differential amplifier 2 approaches 0V. That is, the output voltage Vop is prevented from sticking to the high voltage side or the negative voltage side, and the dynamic range of AD conversion can be improved. Further, the contents of the offset register of each channel of the offset register group 10 are updated so as to approach the zero value.

  In this embodiment, the offset measurement is repeated up to 5 cycles. When the measurement ends in the 5th cycle, the AD conversion data stored in the offset register of each channel of the offset register group 10 at that time is the final offset data. Become. This offset data is obtained by adding the offset of the bridge sensor, the offset of the high gain differential amplifier 2, and the offset of the successive approximation AD converter main body 3 for each channel.

  Next, when AD conversion is performed on the actual measurement detection signals of the bridge sensors B1 to B3, the reference voltage VCOM is set to the voltage value obtained in the final cycle (the fifth cycle in the above) for each channel, and the offset register group The offset data stored in the offset register of each of the ten channels is input to the data differentiator 11. Therefore, when the AD conversion data of the actual measurement detection signal of each channel is output from the successive approximation AD conversion main body 3, the offset data of each channel is subtracted from the AD conversion data of each channel, and finally the offset is compensated. AD conversion data is output.

  Note that the pitch of the reference voltage VCOM adjusted in the reference voltage encoder 8 is not limited to 100 mV described in this embodiment. As the adjustment voltage is made smaller than 100 mV, the optimum reference voltage VCOM for setting the output voltage Vop of the high gain differential amplifier 2 to the intermediate potential (= 0 V) can be set with higher accuracy. Ideally, the offset register group 10 need not be provided. However, since the types of output voltages from the reference voltage encoder 8 increase, the area increases.

  According to the present embodiment, since the output voltage Vop when the non-measurement detection signal of the bridge sensor is input approaches the intermediate voltage by the set reference voltage VCOM, the output voltage Vop obtained when the actual measurement detection signal is input is high potential. Sticking to the power supply voltage side or the low potential voltage side is prevented, and the dynamic range of AD conversion can be maximized.

In addition, since the reference voltage VCOM of the high gain differential amplifier 2 is set to an optimum value according to the bridge sensor of each channel, the bridge sensor, the high gain differential amplifier 2, and the successive approximation AD conversion main body 3 are included. Can compensate for the offset of the entire system.

Further, in addition to the adjustment of the reference voltage VCOM, if offset data is stored in the offset register of each channel of the offset register group 10 and subtracted from the AD conversion data when the actual measurement detection signal is input, it is possible to completely Since close offset compensation can be performed, in this case, it is not necessary to make the resolution of the reference voltage fine, and an increase in area when integrated circuits can be avoided.

1: Multi-input multiplexer 2: High-gain differential amplifier 3: Successive comparison AD conversion main body 4: Sample hold circuit 5: Comparator 6: Successive comparison register 7: DA converter 8: Reference voltage encoder 9: Buffer 10: Offset register group 11: Data differentiator

Claims (4)

A successive conversion AD that obtains AD conversion data by comparing and amplifying the detected signal of a sensor that outputs a measured value of a physical phenomenon as an electrical detection signal with a reference voltage, and AD-converting the comparatively amplified voltage using a successive approximation type In the conversion method,
When a non-measurement detection signal is input from the sensor,
In the first cycle, the first voltage is set as the reference voltage to obtain the AD conversion data,
In the n-th cycle (n is a positive integer less than or equal to 2 and less than m (m is a positive integer greater than or equal to 3)), depending on the polarity bit of the AD conversion data obtained in the n-1th cycle, the AD As the reference voltage, the nth voltage obtained by raising or lowering the n-1 voltage by a predetermined voltage is set as the reference voltage so as to obtain AD conversion data of the nth cycle. ,
In the mth cycle, according to the polarity bit of the AD conversion data obtained in the m−1th cycle, the m−1th voltage is set as the reference voltage so that the AD conversion data approaches a zero value. Set the mth voltage increased or decreased by the predetermined voltage,
When an actual measurement detection signal is input from the sensor, the m-th voltage is set as the reference voltage and the AD conversion data is obtained by obtaining the AD conversion data,
A plurality of the sensors are provided, and each sensor is switched and processed in each cycle.
When the actual measurement detection signal is input from the sensor, the m-th voltage of the sensor is set as the reference voltage.
The successive approximation type AD conversion method according to claim 1,
When a non-measurement detection signal is input from each sensor, the AD conversion data obtained when the mth voltage is set as the reference voltage is stored as offset data for each sensor, and actual measurement is performed from the sensor. A successive conversion AD conversion method , wherein when the detection signal is input, the offset data corresponding to the sensor is subtracted from the AD conversion data corresponding to the sensor . A sensor that outputs a measurement value of a physical phenomenon as an electrical detection signal, a high-gain differential amplifier that compares and amplifies the detection signal of the sensor with a reference voltage, and AD-converts the output voltage of the high-gain differential amplifier for AD In a successive approximation type AD conversion apparatus including a successive approximation type AD conversion main body that outputs conversion data,
When a non-measurement detection signal is input from the sensor, a reference voltage encoder is provided for increasing or decreasing the reference voltage at a predetermined voltage pitch according to the polarity bit of the AD conversion data output from the successive approximation AD conversion main body. ,
When a non-measurement detection signal is input from the sensor, the reference voltage encoder sets the first voltage as the reference voltage in the first cycle, and the nth (n is 2 or more and m (m is 3 or more). In the cycle of a positive integer) less than a positive integer), the reference voltage is set so that the AD conversion data approaches a zero value according to the polarity bit of the AD conversion data obtained in the (n-1) th cycle. , The nth voltage obtained by raising or lowering the n-1 voltage by a predetermined voltage is set, and in the mth cycle, according to the polarity bit of the AD conversion data obtained in the m-1st cycle, As the reference voltage, an m-th voltage obtained by increasing or decreasing the m-1 voltage by the predetermined voltage is set so that the AD conversion data approaches a zero value, and an actual measurement detection signal is output from the sensor. As you type , Sets the voltage of the first m as the reference voltage, a successive approximation type AD converter,
A plurality of the sensors are provided, and each sensor is switched and processed in each cycle.
When the actual measurement detection signal is input from the sensor, the m-th voltage of the sensor is set as the reference voltage in the reference voltage encoder.
In the successive approximation AD converter according to claim 3,
When a non-measurement detection signal is input from each sensor, the AD conversion data obtained when the mth voltage is set as the reference voltage in the reference voltage encoder is stored as offset data for each sensor. Offset register,
A plurality of data differentiators for subtracting offset data stored in the offset register corresponding to the sensor from AD conversion data corresponding to the sensor when an actual measurement detection signal is input from each sensor;
A successive conversion AD converter characterized by comprising:

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